1. Field of the Invention
This invention relates to an arcuate mooring line fairlead, preferably of substantially quadrant shape, which is stably self-aligning with a stretch of line extending beyond the fairlead.
2. The Problem
The fairlead of the present invention is used in conjunction with lines to be guided such as mooring lines of large diameter which are under heavy, fluctuating loads. Such lines are used, for example, to moor floating oil drilling rigs, construction platforms or processing platforms and, consequently, are almost continuously working as the result of wind, wave, tide and current action. Such working is conducive to wear of any line guide apparatus and to chafing and ultimate failure of even large mooring lines if they are not properly guided and protected. Such large cables are subject to fatigue failure if they are bent on a curvature of small radius for an extended period of time. The problem is aggravated by such lines being redirected by some type of guide apparatus through a substantial arc, such as from about 45 degrees to about 180 degrees, for example, between vertical and near horizontal or from horizontal to almost directly downward.
3. Prior Art
A quadrant type of self-aligning fairlead is disclosed in the roller sheave of U.S. Pat. No. 1,712,478, issued May 7, 1929, but such sheave is not stably self-aligning in the sense that tilting of the sheave about the axis of the arc is not restrained.
Also, U.S. Pat. No. 4,260,119, issued Apr. 7, 1981, shows a quadrant fairlead of the roller type generally as in U.S. Pat. No. 1,712,478, but it is not self-aligning.
U.S. Pat. No. 4,430,023, issued Feb. 7, 1984, shows an arcuate rope guide tube of the contiguous contact surface type rather than of the roller type, but it is not self-aligning and has an undesirably small passage through it.
A self-aligning pulley for a line is shown in U.S. Pat. No. 1,805,800, issued May 19, 1931.